Agreed...bad habit to get into. Flowering plants tend to freak if you wake them in the middle of nap time.
The only thing I can think of that will possibly fluctuate enough to worry about during the dark period is temperature. (and CO2, if running it) But you can check on 'em just before lights come on without much worry. I'd say no more than 5 minutes before lights on, but this is my own arbitrary guideline.

emptyfarmer420:
Which shade of green works best? Do you use a special bulb?
Rusty Trichome Reviewed by Rusty Trichome on . Can I check my plants when lights out? I tried to find something about this by searching the forums (really) but could not find anything. I waked and baked so please bear with me...:stoned: I am just starting to flower 12/12 and was wondering if checking on the plants (like for pH, PPM, and water top ups) during the dark period is bad. I can get the outside room fairly dark and would use a flashlight to see (I have a small grow tent in a large room). So, would doing this for 5 minutes or so cause stress? Buzz Rating: 5